The present invention relates to a method for preparing vinyl chloride polymers and more specifically to a method for preparing vinyl chloride polymers which makes it possible to provide polymeric products having high quality in a high yield.
It has been known that, when preparing vinyl chloride polymers, for instance, according to suspension polymerization in an aqueous medium, a polymerization initiator which is charged into a polymerizer through a piping and/or an opening for charging the same into the polymerizer is adhered to and/or remains in the piping and/or the opening and reacts with monomers during the polymerization to form polymer scales on these portions. The polymer scales gradually grow during the polymerization to thereby cause clogging of the piping and/or the opening for charging the polymerization initiator into the polymerizer. Therefore, it is often necessary to stop the operation of the polynerizer in order to remove the resultant polymer scales from the piping and/or the opening. Under such circumstances, there have been proposed various methods for preventing the formation of such polymer scales on the inner wall of the piping and/or at the opening for charging the polymerization initiator or removing such polymer scales formed thereon. Examples of such methods comprise the steps of, for instance, washing the piping and/or the opening with a solvent for polymerization initiator or washing these portions of the polymerizer with a solvent and then closing the opening.
However, in the method comprising simply washing the piping and/or the opening with a solvent, if a large amount of solvent is used to remove such polymerization initiator attached to the wall of the piping and/or the opening of the polymerizer, the solvent possibly remains in vinyl chloride polymer as the final product. The solvent remaining in the polymer leads to the reduction in the quality of the final products and giving out a bad smell during fabrication of the vinyl chloride polymer. For this reason, the solvent must used in a limited amount, but this in turn leads to insufficinet removal of the polymerization initiator attached these portions and as a result, more or less the polymerization initiator remains at the opening and/or the piping for charging the same into the polymerizer. Therefore, if the polymerization is continued for a long period of time, the polymer scales grow due to monomers attached to such portions and the opening and the piping for charging it into the polymerizer are finally clogged or closed.
On the other hand, in the latter method in which these portions are washed to some degree and thereafter the opening for charging the polymerization initiator into a polymerizer is closed, a small amount of monomers penetrate into the opening through a closure therefor to likewise form polymer scales and thus the opening and/or the piping are clogged or closed.
Moreover, there has been proposed a method for preparing vinyl chloride polymers in which a polymerization initiator is charged into a polymerizer in the form of an aqueous emulsion in order to eliminate the necessity of using a solvent for washing the piping and/or the opening of the polymerizer.
However, in such a method utilizing polymerization initiator in the form of an aqueous emulsion, the initiator is sometimes attached to or remains in such portions. Therefore, if the polymerization operation is continued for a long period of time, polymer scales are possibly formed on the portions and consequently the opening and/or the piping for charging the polymerization initiator are clogged or closed. Therefore, there is a demand for the development of novel and effective solutions of the problems concerning the formation of polymer scales.